1. Field of the Invention
The present invention relates to a circuit board and a method of manufacturing the same, and in more detail to a circuit board with a core substrate, a method of manufacturing the same, a semiconductor device that uses a circuit board, and a prepreg used in a circuit board.
2. Related Art
Circuit boards used to mount semiconductor elements include boards with a core substrate made of carbon fiber reinforced plastic (CFRP). A core substrate made of CFRP has a low thermal expansion coefficient compared to a conventional core substrate made of a glass epoxy substrate. A circuit board that uses a CFRP core substrate can be manufactured so that the thermal expansion coefficient matches the thermal expansion coefficient of a semiconductor element, which is effective in avoiding thermal stress that is produced between the semiconductor element and the circuit board.
A circuit board is formed by laminating wiring layers on both surfaces of the core substrate and forming PTH (Plated Through Holes) to conduct electricity between the wiring layers laminated on both surfaces of the core substrate. These PTH are formed by forming through holes in the substrate and then carrying out plating to form conductive parts (a plated layer) on the inner wall surfaces of the through holes.
However, for a core substrate with a core portion of a material like CFRP that conducts electricity, if through holes are simply formed in the substrate and the inner wall surfaces of such through holes are plated, electrical shorting will occur between the PTH and the core portion. For this reason, when forming PTH in a core substrate with a core portion that conducts electricity, preliminary holes are formed through the core substrate with a larger diameter than the PTH, the preliminary holes are filled with an insulating resin, and then the PTH are formed inside the preliminary holes to prevent shorting between the PTH and the core portion (see Patent Documents 1, 2).    Patent Document 1            Japanese Laid-Open Patent Publication No. 2003-218287            Patent Document 2            Japanese Domestic Republication No. 2004/064467        